Approaching the 1.5 °C warming threshold and escalating seasonal warm extremes in the Yangtze River Basin

The Yangtze River Basin (YRB), a pivotal strategic development region in China, has experienced escalating risks of warm extremes in recent years, profoundly impacting socioeconomic structures and ecosystems. The scarcity of high-resolution gridded observational data from the late 19th and early 20th centuries has hindered comprehensive research on long-term trends and warm extremes of seasonal near-surface air temperature (SAT), particularly for assessing the temperature control target of the International Paris COP21 Agreement. This study evaluates changes in the seasonal SAT trends and WMO 25-years return period warm extremes using spatially downscaled, and bias-corrected grid-weighted ensemble of simulations derived from the Coupled Model Intercomparison Project phase 6 (CMIP6), from 1850 to 2100. Furthermore, the record-breaking 2022 summer heatwave underscores the urgency of understanding future probabilities of such events. –Our analysis reveals significant regional warming across four seasons, with the annual SAT approaching the Paris Agreement’s 1.5 °C threshold above pre-industrial levels. Under the SSP2–4.5 scenario, the summer warming rate is projected to accelerate 3–4 times faster during 2024–2100 compared to the historical period (1850–2023). Future warm summer extremes similar to the 2022 event are expected to intensify 0.5–2 times. The recurrence probability of warm extremes across all seasons surpassing their historical thresholds is projected to range from 58 % to 81 % across the YRB, and the upper reach is expected to be highly prone to these warm extremes. Graphical Abstract • The Yangtze River Basin (YRB) is hurtling towards its annual temperature approaching 1.5 °C above the pre-industrial levels. • The YRB will face extremes approximately 0.5–2 times stronger than the heatwave of 2022 during 2024–2100. • The probability of seasonal extremes exceeding historical thresholds is projected to 58 % (SSP2–4.5) and 70 % (SSP5–8.5).